Flexible Skin Based Patient Tracker For Optical Navigation

ABSTRACT

A skin-based patient tracking apparatus for surgical navigation. The apparatus includes an adhesive layer, a plurality of surgical tracking elements, a base layer between the adhesive layer and the plurality of surgical tracking elements, and an outer layer covering the plurality of surgical tracking elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/663,034 filed on Mar. 19, 2015, now U.S. Pat. No. 10,413,377 issuedon Sep. 17, 2019, the entire disclosure of which is incorporated hereinby reference.

FIELD

The present disclosure relates to a flexible skin-based patient trackingapparatus for optical surgical navigation.

BACKGROUND

This section provides background information related to the presentdisclosure, which is not necessarily prior art.

In an anatomy, such as a human anatomy, various anatomical portions andfunctions may be damaged or require repair after a period of time. Theanatomical portion or function may be injured due to wear, aging,disease, or exterior trauma. To assist the patient, a procedure may beperformed that may require access to an internal region of the patientthrough an incision. Due to exterior soft tissue, visualization ofportions of the interior of the anatomy may be difficult or require alarge opening in the patient.

Image data may be required of a patient to assist in planning,performing, and post-operative analysis of a procedure. For example,magnetic resonance image data can be acquired of the patient to assistin diagnosing and planning a procedure. The image data acquired of thepatient can also be used to assist in navigating various instrumentsrelative to the patient while performing a procedure.

It is known to fixedly interconnect fiducial markers or tracking deviceswith a patient while imaging the patient and substantially using thefiducial markers that are imaged in the image data to correlate orregister the image data to a patient space and the tracking devices forsubsequent tracking. The fiducial markers and/or tracking devices aresometimes invasively fixed directly to the patient. While such fiducialmarkers and/or tracking devices are suitable for their intended use,they are subject to improvement. For example, it may be desirable to:minimize the invasiveness of the fiducial markers and/or trackingdevices on the patient; not limit registration to the specific discretelocations of implanted fiducial markers; overcome issues presented whenthe fiducial markers and/or tracking devices are obscured duringsurgery; and generally increase the accuracy of the fiducial markersand/or tracking devices. An improved patient tracker would also bedesirable. The present teachings are directed to an improved patienttracker that may be an improved fiducial as well.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

The present teachings provide for a skin-based patient trackingapparatus for surgical navigation. The apparatus generally includes anadhesive layer, a plurality of surgical tracking elements, a base layerbetween the adhesive layer and the plurality of surgical trackingelements, and an outer layer covering the plurality of surgical trackingelements.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is an environmental view of a surgical navigation systemaccording to the present teachings;

FIG. 2 illustrates a flexible skin-based patient tracker for surgicalnavigation according to the present teachings secured to a back of apatient;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 4 illustrates the flexible skin-based patient tracker of FIG. 2with an incision therethrough;

FIG. 5 illustrates the flexible skin-based patient tracker of FIG. 2stretched at an upper left-hand corner thereof in response to movementof the patient's left shoulder; and

FIG. 6 illustrates a method according to the present teachings fortracking patient movement during surgery.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

With initial reference to FIG. 1, a surgical navigation system accordingto the present teachings for use during various procedures is generallyillustrated at reference numeral 10. The system 10 can be used to tracklocation of a device 12 relative to a patient 14 to assist in theimplementation of, or the performance of, any suitable surgicalprocedure. The device 12 can be any suitable surgical device, such asany suitable probe including a pointer probe, a catheter, a needle, alead, an electrode implant, a cutting instrument, etc. More specificexamples include ablation catheters, deep brain stimulation (DBS) leadsor electrodes, microelectrode (ME) leads, electrodes for recording, etc.Moreover, the navigated device 12 may be used in any region of the body,in addition to the back as illustrated. The navigation system 10 and thevarious devices 12 may be used in any appropriate procedure, such as aminimally invasive procedure, arthroscopic procedure, percutaneousprocedure, stereotactic procedure, or an open procedure.

Although an exemplary navigation system 10 including an imaging system16 is discussed herein, one skilled in the art will understand that thepresent teachings are merely for clarity of the present discussion andexemplary purposes, and that any appropriate imaging system, navigationsystem, patient specific data, and non-patient specific data can beused. For example, the intraoperative imaging system can include an MRIimaging system, such as the PoleStar® MRI imaging system or an O-arm®imaging system sold by Medtronic, Inc. having a place of business inMinnesota, USA. It will be understood that the navigation system 10 canincorporate or be used with any appropriate preoperatively orintraoperatively acquired image data.

The navigation system 10 can include the optional imaging device 16 thatis used to acquire pre-, intra-, or post-operative, including real-time,image data of the patient 14. In addition, data from atlas models can beused to produce images for navigation, though they may not be patientimages. Although, atlas models can be morphed or changed based uponpatient specific information. Also, substantially imageless systems canbe used, such as those disclosed in U.S. patent application Ser. No.10/687,539, filed Oct. 16, 2003, now U.S. Pat. App. Pub. No.2005/0085714, entitled “METHOD AND APPARATUS FOR SURGICAL NAVIGATION OFA MULTIPLE PIECE CONSTRUCT FOR IMPLANTATION”, incorporated herein byreference. Various systems can use data based on determination of theposition of various elements represented by geometric shapes.

The optional imaging device 16 is, for example, a fluoroscopic X-rayimaging device that may be configured as a C-arm 18 having an X-raysource 20, an X-ray receiving section 22, an optional calibration andtracking target 24 and optional radiation sensors. The calibration andtracking target 24 includes calibration markers (not illustrated). Imagedata may also be acquired using other imaging devices, such as thosediscussed above and herein.

An optional imaging device controller 26 may control the imaging device16, such as the C-arm 18, which can capture the X-ray images received atthe receiving section 22 and store the images for later use. Thecontroller 26 may also be separate from the C-arm 18 and can be part of,or incorporated into, a workstation 28. The controller 26 can controlthe rotation of the C-arm 18. For example, the C-arm 18 can move in thedirection of arrow 30 and/or rotate about the patient 14 in any suitablemanner, allowing anterior or lateral views of the patient 14 to beimaged. The movements of the imaging device 16, such as the C-arm 18,can be tracked with a tracking device 34. As discussed herein, thetracking device 34, according to various embodiments, can be anyappropriate tracking device to work with any appropriate tracking system(e.g. optical, electromagnetic, acoustic, etc.). Therefore, unlessspecifically discussed otherwise, the tracking device 34 can be anyappropriate tracking device.

In the example of FIG. 1, C-arm 18 can be positioned in any suitablemanner to permit images of the patient 14 to be taken from multipledirections or in multiple planes. An example of a fluoroscopic C-armX-ray device that may be used as the optional imaging device 16 is the“Series 9600 Mobile Digital Imaging System,” from GE Healthcare,(formerly OEC Medical Systems, Inc.) of Salt Lake City, Utah. Otherexemplary fluoroscopes include bi-plane fluoroscopic systems, ceilingmounted fluoroscopic systems, cath-lab fluoroscopic systems, fixed C-armfluoroscopic systems, isocentric C-arm fluoroscopic systems,three-dimensional (3D) fluoroscopic systems, intraoperative O-arm™imaging systems, etc.

The C-arm imaging system 18 can be any appropriate system, such as adigital or CCD camera, which are well understood in the art.Two-dimensional fluoroscopic images that may be taken by the imagingdevice 16 are captured and stored in the C-arm controller 26. Multipletwo-dimensional images taken by the imaging device 16 may also becaptured and assembled to provide a larger view or image of a wholeregion of the patient 14, as opposed to being directed to only a portionof a region of the patient. For example, multiple image data or sets ofdata of a patient's back, leg, cranium, and brain may be appendedtogether to provide a full view or complete set of image data of theback, leg, or brain that can be later used to follow contrast agent,such as bolus or therapy tracking. The multiple image data can includemultiple two-dimensional (2D) slices that are assembled into a 3D modelor image.

The image data can then be forwarded from the C-arm controller 26 to thenavigation computer and/or processor controller or workstation 28 havinga display device 36 to display image data 38 and a user interface 40.The workstation 28 can also include or be connected to an imageprocessor, a navigation processor, and a memory to hold instructions anddata. The workstation 28 can also include an optimization processor thatassists in a navigated procedure. It will also be understood that theimage data is not necessarily first retained in the controller 26, butmay also be directly transmitted to the workstation 28. Moreover,processing for the navigation system and optimization can all be donewith single or multiple processors all of which may or may not beincluded in the workstation 28.

The workstation 28 provides facilities for displaying the image data 38as an image on the display device 36, saving, digitally manipulating, orprinting a hard copy image of the received image data. The userinterface 40, which may be a keyboard, mouse, touch pen, touch screen orother suitable device, allows a physician or user 42 to provide inputsto control the imaging device 16, via the C-arm controller 26, or adjustthe display settings of the display 36. The workstation 28 may alsodirect the C-arm controller 26 to adjust the C-arm 18 to obtain varioustwo-dimensional images in different planes in order to generaterepresentative two-dimensional and three-dimensional images.

While an exemplary optional imaging device 16 is shown in FIG. 1, anyother alternative 2D, 3D or 4D imaging modality may be used. Forexample, any 2D, 3D or 4D imaging device, such as isocentricfluoroscopy, bi-plane fluoroscopy, ultrasound, computed tomography (CT),multi-slice computed tomography (MSCT), magnetic resonance imaging(MRI), positron emission tomography (PET), optical coherence tomography(OCT) (a more detailed discussion on optical coherence tomography (OCT),is set forth in U.S. Pat. No. 5,740,808, issued Apr. 21, 1998, entitled“Systems And Methods For Guiding Diagnostic Or Therapeutic Devices InInterior Tissue Regions” which is hereby incorporated by reference).Intra-vascular ultrasound (IVUS), intraoperative CT, single photoemission computed tomography (SPECT), planar gamma scintigraphy (PGS).Additional imaging systems include intraoperative MRI systems such asthe PoleStar® MRI imaging system. Further systems include the O-Arm®imaging system. The images may also be obtained and displayed in two,three or four dimensions. In more advanced forms, four-dimensionalsurface rendering regions of the body may also be achieved byincorporating patient data or other data from an atlas or anatomicalmodel map or from pre-operative image data captured by MRI, CT, orechocardiography modalities.

Image datasets from hybrid modalities, such as positron emissiontomography (PET) combined with CT, or single photon emission computertomography (SPECT) combined with CT, could also provide functional imagedata superimposed onto anatomical data to be used to confidently reachtarget sights within the patient 14. It should further be noted that theoptional imaging device 16, as shown in FIG. 1, provides a virtualbi-plane image using a single-head C-arm fluoroscope as the optionalimaging device 16 by simply rotating the C-arm 18 about at least twoplanes, which could be orthogonal planes to generate two-dimensionalimages that can be converted to three-dimensional volumetric images. Byacquiring image data in more than one plane, an icon representing thelocation of an impactor, stylet, reamer driver, taps, drill, DBSelectrodes, ME electrodes for recording, probe, or other instrument,introduced and advanced in the patient 14, may be superimposed in morethan one view on display 36 allowing simulated bi-plane or evenmulti-plane views, including two and three-dimensional views.

With continuing reference to FIG. 1, the navigation system 10 canfurther include a tracking system, such as, but not limited to, anelectromagnetic (EM) tracking system 46A or an optical tracking system46B. Either or both can be used alone or together in the navigationsystem 10. Moreover, discussion of the EM tracking system 46A can beunderstood to relate to any appropriate tracking system. The opticaltracking system 46B can include the Stealthstation® Treatment GuidanceSystem including the Treon® Navigation System and the Tria® NavigationSystem, both sold by Medtronic Navigation, Inc. Other tracking systemsinclude acoustic, radiation, radar, infrared, etc.

The EM tracking system 46A includes a localizer, such as a coil array 48and/or second coil array (not shown), a coil array controller 52, anavigation probe interface 54, a device 12 (e.g. catheter, needle,pointer probe, or instruments, as discussed herein), and can include adynamic reference frame including a tracking device, such as patienttracking apparatus 110, which is described herein as an optical trackingapparatus, but may be an electromagnetic tracking apparatus as oneskilled in the art will appreciate. An instrument tracking device 34Acan also be associated with, such as fixed to, the device 12 or aguiding device for an instrument.

The tracking devices 34 and 34A, or any other tracking device asdiscussed herein, can include a sensor, a transmitter, or combinationsthereof. The tracking devices 34 and 34A can be either EM trackingdevices or optical tracking devices, such as reflective tracking arrays.Further, the tracking devices 34/34A can be wired or wireless to providea signal emitter or receiver within the navigation system. For example,the tracking devices 34 and 34A can include an electromagnetic coil tosense a field produced by the localizing array 48. Nevertheless, onewill understand that the tracking devices 34 and 34A can receive asignal, transmit a signal, or combinations thereof to provideinformation to the navigation system 10 to determine a location of thetracking devices 34 and 34A. The navigation system 10 can then determinea position of the instrument or tracking device 34A to allow fornavigation relative to the patient and patient space.

It should further be noted that the entire tracking system 46A, 46B orparts of the tracking system 46A, 46B may be incorporated into theimaging device 16, including the workstation 28. Incorporating thetracking system 46A, 46B may provide an integrated imaging and trackingsystem. This can be particularly useful in creating a fiducial-lesssystem. Moreover, fiducial marker-less systems can include a trackingdevice and a contour determining system, including those discussedherein. Any combination of these components may also be incorporatedinto the imaging system 16, which again can include a fluoroscopic C-armimaging device or any other appropriate imaging device.

The EM tracking system 46A uses the coil arrays 48 to create anelectromagnetic field used for navigation. The coil arrays 48 caninclude a plurality of coils that are each operable to generate distinctelectromagnetic fields into the navigation region of the patient 14,which is sometimes referred to as patient space. Representativeelectromagnetic systems are set forth in U.S. Pat. No. 5,913,820,entitled “Position Location System,” issued Jun. 22, 1999 and U.S. Pat.No. 5,592,939, entitled “Method and System for Navigating a CatheterProbe,” issued Jan. 14, 1997, each of which are hereby incorporated byreference. Further operation of the EM tracking system 46A is providedin U.S. Pat. No. 8,467,852 titled “Method and Apparatus for Performing ANavigated Procedure,” which is assigned to Medtronic, Inc. and isincorporated herein by reference.

Briefly, the navigation system 10 operates as follows. The navigationsystem 10 creates a translation map between all points in the image datagenerated from the imaging device 16 which can include external andinternal portions, and the corresponding points in the patient's anatomyin patient space. After this map is established, the image space isregistered to patient space in any suitable manner. Examples ofautomatic registration are set forth in: U.S. Pat. No. 6,477,400 titled“Fluoroscopic Image Guided Orthopaedic Surgery System withIntraoperative Registration,” which issued on Nov. 5, 2002 and isincorporated herein by reference; and U.S. Pat. No. 8,238,631 titled“System and Method for Automatic Registration between an Image and aSubject,” which issued on Aug. 7, 2012 to Medtronic Navigation, Inc.,and is incorporated herein by reference. Registration can also takeplace by performing the imaging with the patient tracking apparatus 110secured to the patient as described herein.

Whenever the tracked device 12 is used, the workstation 28 incombination with the optical tracking system 46B (or optionally the EMtracking system 46A) uses the translation map to identify thecorresponding point on the image data or atlas model, which is displayedon display 36. This identification is known as navigation orlocalization. An icon representing the localized point or instruments isshown on the display 36 within several two-dimensional image planes, aswell as on three and four dimensional images and models.

To enable navigation, the navigation system 10 must be able to detectboth the position of the patient's anatomy as determined using thepatient tracking apparatus 110, for example, in the manner describedherein, and the position of the device 12 or an attachment member (e.g.,tracking device 34A) attached to the device 12. Knowing the location ofthese two items allows the navigation system 10 to compute and displaythe position of the device 12 or any portion thereof in relation to thepatient 14. The tracking systems 46A and 46B are employed to track thedevice 12 and the anatomy of the patient 14 simultaneously.

The patient tracking apparatus 110 described herein is fixed to thepatient 14 to identify the location of the patient in the navigationfield. Thus, the patient tracking apparatus 110 acts as a dynamicreference frame, and may operate as a fiducial as described herein,during registration. The optical tracking system 46B continuouslycomputes or calculate the relative position of the patient trackingapparatus 110 and the device 12 during localization and relates thisspatial information to patient registration data to enable navigation ofthe device 12 within and/or relative to the patient 14. Navigation caninclude image guidance or imageless guidance.

Patient registration is the process of determining how to correlate theposition of the device 12 relative to the patient 14, to the position onthe diagnostic or image data. To register the patient 14, the physicianor user 42 may select and store one or more particular points from theimage data and then determine corresponding points on the patient'sanatomy. The navigation system 10 analyzes the relationship between thepoints and computes a match, which correlates every point in the imagedata with its corresponding point on the patient's anatomy or thepatient space.

The points that are selected to perform registration can be imagefiducial points. The image fiducial points can be produced by thepatient tracking apparatus 110 described herein. The image fiducialpoints are identifiable in the image data and identifiable andaccessible on the patient 14. The anatomical landmarks can includeindividual or distinct points on the patient 14 or contours (e.g.three-dimensional contours) defined by the patient 14.

A processor, such as a processor within the workstation 28, candetermine registration of the patient space to the image space. Theregistration can be performed according to generally known mapping ortranslation techniques. The registration can allow a navigated procedureusing the image data.

With continued reference to FIG. 1 and additional reference to FIGS. 2and 3, the patient tracking apparatus 110 will now be further described.The patient tracking apparatus 110 generally includes a base layer 112,which can be made of any suitable material, to provide a flexible sheet.An adhesive layer 114 is on a first side of the base layer 112. Anyadhesive suitable for securing the base layer 112 to skin can be used.While any suitable base layer 112 and adhesive layer 114 can be used, anexemplary base layer including a suitable adhesive is Tagaderm™ from 3MCorporation of Minnesota, USA. The base layer 112 can be of any suitablesize or shape, such as a suitable shape to cover an area of the patient14 to be operated on. The base layer 112 can be a portion of a surgicaldrape 130, as further described herein.

Secured to the base layer 112 are a plurality of tracking elements 116.The tracking elements 116 can be any suitable active or passive trackingelements, such as reflective dots or light emitting diodes (LED's) foruse with the optical tracking system 46B. The tracking elements 116 canbe secured to the base layer 112 in any suitable manner such as with atracking element retention portion 118. The retention portion 118 can beany suitable adhesive, mold, or bond for securing the tracking elements116 to the base layer 112.

Position of the tracking elements 116 in the patient space can bedetermined using the optical tracking system 46B. The tracking elements116 can be arranged in any suitable manner, such as in a plurality orrows and columns as illustrated. Any suitable number of trackingelements 116 can be used. For example, the tracking elements 116 can bearranged in rows of ten tracking elements 116 and columns of fifteentracking elements 116 as illustrated in FIGS. 2, 4, and 5 for a total ofone hundred and fifty tracking elements 116. The tracking elements 116can be spaced apart at any known suitable distance, such as about 2 cm.

The tracking elements 116 can be covered with an outer layer or cover120. The cover 120 can be any suitable cover, such as any suitabletransparent cover 120. The cover 120 protects the tracking elements 116from damage, and can prevent the tracking elements 116 from becomingdirty. The cover 120 can be easily cleaned, such as by wiping with wateror a suitable solvent, to allow light directed to the tracking elementsby the optical tracking system 46B to be reflected by the trackingelements 116. The cover 120 can be made of any suitable material, suchas a hydrophobic transparent material that, for example, repels bodilyfluids and can be easily cleaned.

As illustrated in FIGS. 2, 4, and 5, for example, the patient trackingapparatus 110 can include a surgical drape 130. The surgical drape 130can be incorporated into the patient tracking apparatus 110 in anysuitable manner. For example, base layer 112 can be part of the surgicaldrape 130. The surgical drape 130 can extend from, and generallysurround, an area of the patient tracking apparatus 110 including thetracking elements 116. The surgical drape 130 can be sterile, and cancover an area of the patient surrounding the surgical site. The surgicaldrape 130 can be of any suitable size or shape depending on theprocedure for which the surgical drape 130 is to be used. Thus, thesurgical drape 130 can be a procedure specific surgical drape.

With reference to FIGS. 2, 4, and 5, an exemplary use of the patienttracking apparatus 110 to cover, act as a fiducial, and track movementof, a patient's back during spinal surgery will now be described. Use ofthe apparatus 110 in conjunction with spinal surgery is illustrated anddescribed for exemplary purposes only. The apparatus 110 can be used inconjunction with any suitable procedure at any suitable location on thepatient's body. For example, the apparatus 110 can cover a portion ofthe patient's head during spinal surgery, and can cover a patient'schest during heart surgery.

The patient tracking apparatus 110 is secured to the patient's back overthe area to be operated on with the adhesive layer 114. An incision 140(FIG. 4) into the patient is made directly through the patient trackingapparatus 110. Due to the incision 140, the patient's skin surroundingthe incision 140 will move outward from the incision 140. Because thepatient tracking apparatus 110 is adhesively secured to the patient'sskin, the portions of the apparatus 110 surrounding the incision 140will also move outward, which includes the tracking elements 116.Movement of the tracking apparatus 110 can be detected by the trackingsystem 46B in order to track movement of the patient's skin surroundingthe incision 140. With the patient's spine 142 exposed by the incision140, any suitable spinal operation can be performed.

Any movement of the patient's back can be tracked using the patienttracking apparatus 110. For example and as illustrated in FIG. 5, if thepatient's left shoulder is dipped or moved forward towards a front ofthe patient's body, a upper left hand corner 150 of the apparatus 110will be stretched outward. Thus, the tracking elements 116 at andproximate to the upper left hand corner 150 will be stretched outwardand a separation distance between the tracking elements 116 willincrease at and proximate to the stretched upper left hand corner 150.The stretched position of the tracking elements 116 can be measured bythe optical tracking system 46B.

With additional reference to FIG. 6, a method 210 for using the patienttracking apparatus 110 will now be described. With initial reference toblock 220, the patient tracking apparatus 110 is secured to thepatient's skin with the adhesive layer 114 over any suitable surgicalsite, such as at the patient's back/spine 142. At block 222, the patient14 is imaged in any suitable manner, such as with the imaging system 16,with the patient tracking apparatus 110 secured to the patient 14 sothat the apparatus 110 acts as a fiducial. Alternatively, any othersuitable fiducial can be used.

After the patient 14 is imaged, registration is performed at block 224to register the patient position information to image space about thepatient. Any suitable registration can be used, such as automaticregistration as described in U.S. Pat. Nos. 6,477,400 and/or 8,238,631,or registration using fiducials. Any suitable fiducial can be used, suchas the patient tracking apparatus 110.

After registration is complete, at block 226 the patient trackingapparatus 110 can be used to track position of the patient 14 within thepatient space. For example, the position of each tracking element 116,and the spacing therebetween, is known and entered into any suitableprocessor, such as a processor of the workstation 28. Movement of thepatient's skin will result in movement of the tracking elements 116.Using any suitable technique, such as averaging, changes in location ofthe tracking elements 116 and relative spacing therebetween can be usedto identify changes in the patient's position. For example and withreference to FIG. 5, movement of the patient's left shoulder downward orforward will result in the upper left hand corner 150 of the patienttracking apparatus 110 being stretched, which will cause distancesbetween the tracking elements 116 in the upper left hand corner 150 toincrease and be stretched outward as compared to the rest of thetracking elements 116. This movement of the tracking elements 116 can bedetected by the optical tracking system 46B and measured by theprocessor of the workstation 28, for example. Based on the measurementsand using averaging, the processor can identify movement of the patient14 and update the image data 38 displayed on the display device 36accordingly.

Any other movement of the patient 14 can be detected in a similarmanner, such as movement affecting location of the patient's spine. Forexample, movement of the patient's spine will result in correspondingmovement of the patient's skin over the spine. Movement of the patient'sskin will result in movement of the tracking elements 116 over thepatient's spine, which can be detected using the optical tracking system46B. The processor can then update the image data 38 of the patient'sspine on the display device 36 accordingly.

With reference to FIG. 4, when the incision 140 is made the resultingmovement of the tracking elements 116 can be taken into account whengenerating the image data 38 to eliminate any error. For example, uponmaking the incision 140 the optical tracking system 46B will measure thelocation of the tracking elements 116 and compare their average positionboth before and after the incision 140 is made. Although the trackingelements 116 will move after the incision 140 is made, the averageposition of the tracking elements 116 will remain the same, as will thepatient's skin (assuming that the patient has not moved). Because theaverage position of the tracking elements 116 and the patient's skinwill remain the same, the image data 38 will not need to be modified.Any patient tracking errors that may result due to making the incision140 can advantageously be eliminated.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A system for tracking movement of a patientduring surgery comprising: a skin-based patient tracking apparatus forsurgical navigation including: an adhesive layer including an adhesivematerial configured to stick the skin-based patient tracking apparatusto the patient's skin over a surgical site; a plurality of surgicaltracking elements; a base layer between the adhesive layer and theplurality of surgical tracking elements; and an outer layer covering theplurality of surgical tracking elements; wherein the skin-based patienttracking apparatus is configured to be cut through with an incisionduring surgery to access the surgical site beneath the patient's skin;and wherein the plurality of surgical tracking elements are configuredsuch that an average position of the plurality of surgical trackingelements both before and after the incision is made through theskin-based patient tracking apparatus and into the patient's skin asdetected by a surgical tracking system corresponds to movement of thepatient's skin when the patient tracking apparatus is secured over thesurgical site.
 2. The system of claim 1, wherein the patient trackingapparatus is flexible.
 3. The system of claim 1, wherein the pluralityof surgical tracking elements are optical tracking elements.
 4. Thesystem of claim 1, wherein the surgical tracking elements are bonded tothe base layer.
 5. The system of claim 1, wherein the surgical trackingelements are secured to the base layer with an adhesive.
 6. The systemof claim 1, wherein the surgical tracking elements are molded to thebase layer.
 7. The system of claim 1, wherein the surgical trackingelements are arranged in a plurality of rows and columns.
 8. The systemof claim 1, wherein the outer layer is transparent.
 9. The system ofclaim 1, further comprising a surgical drape integral with the patienttracking apparatus.
 10. The system of claim 1, wherein the base layerincludes a surgical drape extending beyond a portion of the patienttracking apparatus including the plurality of surgical trackingelements.
 11. The system of claim 1, wherein the average position of theplurality of surgical tracking elements is determined by a processor ofthe surgical tracking system.
 12. A system for tracking movement of apatient during surgery comprising: a skin-based patient trackingapparatus for surgical navigation including a plurality of surgicaltracking elements and an adhesive material configured to stick theskin-based patient tracking apparatus to the patient's skin over asurgical site, the skin-based patient tacking apparatus configured to becut through with an incision during surgery to access the surgical sitebeneath the patient's skin; and a surgical tracking system including aprocessor configured to determine an average position of the pluralityof surgical tracking elements both before and after the incision is madethrough the skin-based patient tracking apparatus and into the patient'sskin corresponding to movement of the patient's skin when the patienttracking apparatus is secured over the surgical site.
 13. The system ofclaim 12, wherein the adhesive material is included with an adhesivelayer, a base layer is between the adhesive layer and the plurality ofsurgical tracking elements, and an outer layer covers the plurality ofsurgical tracking elements.
 14. The system of claim 12, wherein theplurality of surgical tracking elements are arranged in a plurality ofrows and columns.
 15. The system of claim 12, wherein the plurality ofsurgical tracking elements are secured to the surgical drape with anadhesive.
 16. The system of claim 15, wherein the plurality of surgicaltracking elements are molded to the surgical drape.
 17. The system ofclaim 12, wherein the patient tracking apparatus is flexible.
 18. Thesystem of claim 12, wherein the surgical tracking system is an opticalsurgical tracking system, and the plurality of surgical trackingelements are optical surgical tracking elements.